This invention relates generally to machines for forming, filling and sealing packages made from an elongated thin flat strip of flexible packaging material, the strip of material being first formed to a depending upwardly open tubular configuration, sealed longitudinally at overlapped vertically extending edge portions, sealed transversely along horizontal lines spaced vertically along the tube, and filled from above with measured quantities of product between successive transverse or end sealing operations. More particularly, the invention relates to an improved servo motor drive means for a tube advancing means and a preliminary flat film advancing means in the machine.
Conventionally, in advancing or feeding a flat strip of packaging material through a tube former, a vacuum or vacuum-friction feed belt mechanism is employed. A pair of perforate endless belts are disposed respectively on opposite sides of the depending tube of packaging material beneath the tube former to engage and draw the same downwardly with gripping action provided by a reduced pressure or vacuum condition at the openings in the belt. The belts may also have substantial frictional engagement with the depending tube of packaging material with a suitable back-up means provided within the tube and a positive intermittent tube advancing operation is thus achieved. It is also a conventional practice to include in machines of the type under consideration a preliminary flat film advancing means interposed between the source of packaging material and the tube former. The preliminary flat film advancing means comprises opposing feed rolls, sometimes referred to in the trade as "measuring rolls", and it is a conventional practice to drive the vacuum tube feeding belts at about a 5% higher speed than the preliminary or measuring rolls. This provides a slight slipping action with efficient tube advancing and forming operation being thus provided.
The following patents relate to the type of vertical form, fill and seal packaging machine under consideration and may be referred to for further description and illustration thereof. U.S. Pat. No. 3,986,921, dated Oct. 19, 1976, entitled SEALING JAW MECHANISM FOR PACKAGE MAKING MACHINE; U.S. Pat. No. 4,023,327, dated May 17, 1977, entitled CONTROL SYSTEM FOR PACKAGE MAKING MACHINE; U.S. Pat. No. 4,040,237, dated Aug. 9, 1977, entitled SEALING JAW MECHANISM FOR PACKAGE MAKING MACHINE; U.S. Pat. No. 4,043,098, dated Aug. 23, 1977, entitled VERTICAL FORM, FILL AND SEAL PACKAGING MACHINE WITH IMPROVED BACK-UP BAR FOR LONGITUDINAL SEALING; U.S. Pat. No. 4,118,913 dated Oct. 10, 1978, entitled SHORT PRODUCT DROP VERTICAL FORM, FILL AND SEAL PACKAGING MACHINE; U.S. Pat. No. 4,128,985; dated Dec. 12, 1978, entitled CONTROL SYSTEM FOR PACKAGE MAKING MACHINE; U.S. Pat. No. 4,136,505, dated Jan. 30, 1979, entitled TUBELESS VERTICAL FORM, FILL AND SEAL PACKAGING MACHINE WITH IMPROVED FEED MEANS; U.S. Pat. No. 4,171,605, dated Oct. 23, 1979, entitled VERTICAL FORM, FILL AND SEAL PACKAGING MACHINE WITH IMPROVED SIDE SEALING MEANS; U.S. Pat. No. 4,291,520, dated Sept. 29, 1981, entitled VERTICAL FORM, FILL AND SEAL PACKAGING MACHINE WITH IMPROVED END SEALING AND STRIPPING MEANS.
In the foregoing patents and in the description and claims which follow terminology such as "package" and "bag" is used and is intended to be generally synonymous with other like terms such as "pouch", "envelope", etc. Terms such as "product" and "charges of product" refer to any of a wide variety of package fill which can be accommodated in vertical form, fill and seal machines. The charges of product may be weighed and successively discharged by an associated product feeder, the feeder may provide a volumetric rather than a weight determination of product charge, and other means may also be employed in introducing charges of product, this even including the manual dumping of product into a depending tube or packaging material.
Packaging machines of the type referred to have been generally satisfactory but in certain instances are found wanting in their maximum speed of operation and in other respects. One limiting factor in providing an efficient high speed packaging machine of the type described resides in the drive means for the machine. Conventionally, an electric motor operates through a speed reducer and a clutch-brake system to drive the preliminary or measuring rolls and the vacuum tube feed belts in common. However, in this type of drive system there are severe limitations on the ability to control acceleration and deceleration characteristics of the intermittent feed operation of the film and tube advancing means. At high speeds, there may be unacceptably sharp acceleration and deceleration characteristics tending to jerk the web or film of packaging material and perhaps causing tracking and even breaking problems. A device referred to as a "web brake" is sometimes employed in providing for precise stopping of the web or film of packaging material particularly where printing of the web or film is required. Such "web brakes" are notoriously difficult to adjust and control even at a 60 (BPM) rate of operation of the machine.
Another problem arising at high speed operation of conventional vertical form, fill and seal machines is in the "hydrostatic shock" which occurs when a heavy product falls within a tube and impinges on a still hot seal and which may involve weakening and even rupture of the seal when the bag comes to a sudden stop with a motor-clutch-brake type drive system.
Inaccuracies in printing on the packaging material may also be encountered at high speed operation with the motor-clutch-brake drive system as well as other detrimental effects on machine operation and product quality.
It is the general object of the present invention to provide a vertical form, fill and seal packaging machine with an improved drive means in the form of a servo motor and control means whereby acceleration and deceleration as well as other characteristics can be precisely programmed and controlled during film and tube advancing operation, the machine speed of operation and efficiency thus being greatly enhanced.